The cerebellum is a region of the brain that plays a major role in the control of movement and cognition. Spinocerebellar Ataxia Type 1 (SCA1) is a fatal human disorder that is one of at least five inherited ataxias, and a total of at least eight neurodegenerative diseases, each caused by the expression of a mutant protein containing an expanded polyglutamine region. Pathogenesis is due to a gain of function conferred by mutant ataxin-1 protein and has been recapitulated in a transgenic mouse model resulting in degeneration of neuronal Purkinje cells in the cerebellum. As a potential approach toward gene therapy for SCA1, we demonstrated during the current period of study: (i) That adeno-associated virus vectors (AAV) are an effective tool for in vivo gene transfer into cerebellar Purkinje cells, yielding up to 3% transduction in a cerebellar hemisphere after a single intracerebellar injection; (ii) That ribozymes and antisense RNAs targeting specific positions in the ataxin message destabilize ataxin message in vitro and in tissue culture cells in vivo, respectively. In this competing renewal application, we propose to extend these studies through the execution of 4 specific aims: (i) Further characterization and optimization of AAV-mediated Purkinje cell transduction in vivo, including the molecular role of basic fibroblast growth factor receptor 1 and heparin sulfate proteoglycan in virus binding, and the relative effectiveness of AAV serotypes 1, 2 and 5 in mediating transduction of cerebellar Purkinje cells; (ii) Further testing of molecular approaches for downregulating or correcting expanded ataxin-1 message, including antisense, ribozyme, trans-splicing and RNA interference; (iii) Establishment of anti-ataxin transgenes, subsequently crossing with SCA1 transgenic mice to evaluate the effectiveness of these approaches in controlling Purkinje cell degeneration and development of ataxia; and (iv) Use of AAV vectors to deliver anti-ataxin or ataxin correcting sequences to cerebellar Purkinje cells in SCA1 transgenic mice, as a direct model of gene therapy for SCA1 in humans. Results from these studies will thus provide optimized molecular tools and delivery conditions which will be applicable to treatment not only of SCA1 but other dominant-acting and other neurologic disorders as well.